FLUID MACHINES

FLUID MACHINE A fluid machine is a device either for converting the energy held by a fluid into mechanical energy or vice versa. Fluid machine may be divided into two groups;

1. Positive displacement group * Reciprocating pump, etc

Part one : Introduction of Pump 1

FLUID MACHINES

2. Rotodynamic group * Pelton wheel, etc

Depend on energy movement; fluid machine could be divided into three categories

1. Pump 2. Turbine 3. Jack

Part one : Introduction of Pump 2

FLUID MACHINES

PUMP INTRODUCTION Rotodynamic pump is essentially a turbine ‘in reverse’; which mean that mechanical energy is transferred from the rotor to the fluid. It is classified according to the direction of the fluid path through them.

1. Radial / centrifugal flow

Part one : Introduction of Pump 3

FLUID MACHINES

2. Axial flow 3. Mixed-flow type

In general usage, the word ‘PUMP’ is applied to a machine dealing with a liquid. A machine in which the working fluid is a gas is more usually termed as fan, blower or compressor.

Part one : Introduction of Pump 4

FLUID MACHINES

HEAD OF PUMP

Part one : Introduction of Pump 5

FLUID MACHINES

CENTRIFUGAL PUMP

This type of pumps is the converse of the

radial-flow (Francis) turbine. Whereas the flow

in the turbine in inwards, the flow in the pumps

is outwards.

The rotor (impeller) rotates inside a spiral

casing. The inlet pipe is axial, and fluid enters

the ‘eye’, that is the center of the impeller with

little, if any, whirl component of velocity.

Part two : Centrifugal Pump 1

FLUID MACHINES

From there it flows outwards in the direction

of the blades, and having received energy from

the impeller, is discharged with increased

pressure and velocity into the casing.

It then has a considerable tangential (whirl)

component of velocity which is normally much

greater than that required in the discharge pipe.

The kinetic energy of the fluid leaving the

impeller is largely dissipated in shock losses

unless arrangements are made to reduce the

velocity gradually.

Part two : Centrifugal Pump 2

FLUID MACHINES

Velocity triangle

Inlet ;

Tangential velocity of impeller

11 rU ω=

Absolute velocity vector at 1α to tangent

1V

Relative velocity to impeller blades

111 UVVr −=

Components velocity of 1V

: whirl velocity 1wV

: radial flow velocity 1fV

Inlet blade angle

1β

Part two : Centrifugal Pump 3

FLUID MACHINES

Outlet ;

Tangential velocity of impeller

22 rU ω=

Absolute velocity vector at 2α to tangent

2V

Relative velocity to impeller blades

222 UVVr −=

Components velocity of 2V

: whirl velocity 2wV

: radial flow velocity 2fV

Inlet blade angle

2β

Part two : Centrifugal Pump 4

FLUID MACHINES

Velocity triangle for centrifugal pump:

Part two : Centrifugal Pump 5

FLUID MACHINES

Calculation is done base on “Euler’s Turbine

Equation”. The one-dimensional theory

simplifies the problem very considerably by

making the following assumptions:

1. The blades are infinitely thin and the

pressure difference across them is replaced

by imaginary body forces acting on the fluid

and producing torque.

2. The number of blades in infinitely large.

Thus, 0=∂∂θv

3. No variation of velocity in the meridional

plane (z-axis). Thus,

In reality, ),,( zrfv θ=

Part two : Centrifugal Pump 6

FLUID MACHINES

Torque = Rate of change of angular momentum

Angular momentum = (Mass) x (Tangential

velocity) x (Radius)

Specific energy, mPgEY&

== (unit : J/kg)

Euler’s Head ;

( )11221 uvuvg

H wwE ⋅−⋅= (unit : m)

Part two : Centrifugal Pump 7

FLUID MACHINES

Relation of u2, vw2 and HE

( )111222 coscos1 αα uvuvg

HE −=

o901 =α 01 =wv and fvv =1

guvH w

E22 ⋅=

Part two : Centrifugal Pump 8

FLUID MACHINES

relation of β2 and HE

from ;

221

22

tan1β

⋅+=⋅

= QCCg

uvH wE

Euler’s head is depends on the value of 2β

Part two : Centrifugal Pump 9

FLUID MACHINES

velocity triangle and the position of blades

Blade condition with has the highest Euler’s head value.

o902 =β

Part two : Centrifugal Pump 10

FLUID MACHINES

Relation of 2β and with Bernoulli equation.

EH

Euler’s head :

gVHHHH w

PVPE 2

22+=+=

Reaction degree of pump =

⎥⎦

⎤⎢⎣

⎡⋅

+=+=22

22

2

tan1

21

21

βUV

gHV

HH f

E

w

P

E

Part two : Centrifugal Pump 11

FLUID MACHINES

LOSSES IN PUMP

3 major types of losses

1. Losses of hydraulic power

a. Circulatory flow

b. Friction

c. Shocking in impeller

2. Loss of volume

3. Loss of mechanical energy

Part three : Losses and Efficiency of Pump 1

FLUID MACHINES

a. Circulatory Flow

SF : Slip Factor

Eideal

actual

w

w

HHH

VVSF

==

′=

2

2

Part three : Losses and Efficiency of Pump 2

FLUID MACHINES

b. Friction losses

2

1 Qkhf ⋅=

: Friction losses fh

: Constant 1k

: Flow rate Q

c. Shock losses

( )22 osh QQkh −=

: Shock losses 2k

: Designed flow rate Q

: Actual flow rate oQ

Part three : Losses and Efficiency of Pump 3

FLUID MACHINES

EFFICIENCY OF PUMP

Overall Efficiency :

i

mo P

gQHρη =

Mechanical Efficiency : [ ]( )i

wwgmech P

UVUVQQg 11221)( −∆+

=ρ

η

Manometric Efficiency :

1122 UVUVgH

ww

mmano −

=η

Volumetric Efficiency :

QQQ

v ∆+=η

Part three : Losses and Efficiency of Pump 4

FLUID MACHINES

Part four : Reaction Turbine – Francis Turbine 6